Light-responsive proteins have evolved to use light efficiently to drive complex processes ranging from photosynthesis to vision. The versatility, selectivity, and efficiency of these photobiological systems serve as an inspiration for technology, driving efforts to develop light-harvesting systems for solar energy applications, light-driven water splitting catalysts for solar energy storage, fluorescent probes for bioimaging, optogenetics tools, photodynamic therapies, and more. To learn from natural light-responsive proteins, however, we need to develop a fundamental understanding of how such systems operate on a molecular level. This requires investigating the light-induced chemical events that occur upon light excitation. Often, this also requires an understanding of how the nuclei and electrons respond to being excited by light. My research therefore involves developing and employing a mix of quantum chemistry and molecular mechanics to understand how chemical and biological systems respond to light. Ultimately, one of our main goals is to derive structure-function relations in photoreceptor proteins that can aid in the design of new light-responsive proteins with potential applications in biotechnology. One example of systems we will investigate are Light-Oxygen-Voltage (LOV) protein domains.